TEXTURAL CHANGES AND MOLECULAR CHARACTERISTICS OF PECTIC CONSTITUENTS IN RIPENING PEACHES

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Abstract
SUMMARY Pectic constituents were isolated from the alcohol insoluble solids of freestone peaches at four stages of ripeness. The varieties studied were Poppy, Loring, Southland and Rio Oso Gem. The pectic substances were fractionated into pectinic acids, pectic acids and protopectin fractions and the molecular weight of each fraction was calculated from its intrinsic viscosity value. The purity and degree of esterification of each fraction were determined. Corresponding shear press firmness values were also measured. Decrease in the molecular weight values of the pectinic acid fraction was found to be closely related to the increase in proportion of pectinic acids with advancing ripeness. A decrease in esterification of the pectic constituents with advancing ripeness was found mainly in the protopectin fraction. These changes were also closely related to the reduction in shear press firmness of the tissue during the ripening process in all varieties of freestone peaches studied. These results seem to provide a basis for studies of enzymatic reactions which influence fruit ripening.

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